LB1111 and Synology Router RT2600ac > No internet in bridge mode

Hello,

I have a Netgear 4g LTE modem/router LB1111.

It is plugged on a Synology router RT2600ac in the WAN port.

If the LB1111 is in router mode, I get my internet working fine.

But if I switch to bridge mode, nothing works any more.

I really can't figure out why.

I followed the Netgear instructions, but nothing works anyway.

My Syno router is set up as:

connexion type : auto (other options are "PPPoE or Manual).

Could someone help me to get over thisd trouble ?

Thanks in advance.